1. Field of the Invention
The present invention relates generally to a surface acoustic wave device and a communication device using the same. More particularly, the present invention relates to a surface acoustic wave device which uses a flip chip bonding technology, can be downsized, and further has high reliability, and a communication device using the same.
2. Description of the Related Arts
In recent years, starting with a portable telephone, a downsizing of a communication device is conspicuous. Together with a tendency of such the downsizing of the device, a demand of a downsizing and a reduction in heights of parts for use therein is increased.
In particular, in the communication device, a filter, a resonator, and a delay line device are essential parts, and the downsizing thereof is realized by a SAW (Surface Acoustic Wave) device using a flip chip bonding technology.
FIGS. 1A and 1B are schematic cross-sectional views showing a method for mounting on a package of such a surface acoustic wave device.
FIG. 1A shows a method for mounting on the package of the surface acoustic wave device by a wire bonding technology. The surface acoustic wave element is formed on a piezoelectric element (chip) 1.
This piezoelectric element 1 is mounted on a package 2 having a recess part formed with a dielectric material such as ceramics, etc., and is pasted and fixed with a conductive adhesive material 3. After the piezoelectric element 1 is mounted on the package 2, it is sealed by a cap 5. Furthermore, a conductor metal plate connected to a ground terminal 4 of the reverse face is provided on an outer surface of the package 2 or metal plating.
Here, an appropriate electrode on the piezoelectric element 1 is connected to an electrode corresponding to the package 2 via an A1 wire 6. Accordingly, a predetermined size is required in a height direction according to the A1 wire 6.
In this manner, in the case of the wire bonding technology shown in FIG. 1A, a reduction in heights is limited. FIG. 1B shows an example using a flip chip bonding technology as a technology for solving this.
In comparison with FIG. 1A, in the flip chip bonding technology of FIG. 1B, an appropriate electrode on the piezoelectric element 1 is connected to an electrode corresponding to the package 2 via an Au bump 7. Accordingly, compared with a height direction in the case of the A1 wire 6, a reduction in heights is possible.
Here, in the flip chip bonding technology of FIG. 1B, a connection face between the piezoelectric element 1 and the package 2 is determined by a size of the Au bump 7, and becomes smaller than the case of the wire bonding technology. On the other hand, a difference in coefficients of linear expansion between the piezoelectric element 1 and the package 2 for general use exists.
For this reason, at the time of a temperature cycle given at a test stage, a stress load applied on the bump 7 is increased. This is a factor (disconnection, etc.) which reduces reliability in the device, and further a factor which prevents that the flip chip bonding technology is adopted for the downsizing.
Accordingly, the present invention solves such problems, and it is an object thereof to provide a surface acoustic wave device which enables a downsizing and high reliability, and a communication device using the same.
In order to solve such a deficiency, according to a first aspect of the present invention there is provided a surface acoustic wave device, comprising a package having a coefficient of linear expansion; and a piezoelectric element forming a surface acoustic wave element, and mounted on the package by a flip chip bonding. The piezoelectric element has different coefficients of linear expansion in a direction of propagation of surface acoustic waves generated by an interdigital electrode of the surface acoustic wave element and in a vertical direction thereto, and further having a long side existing to a direction having a coefficient of linear expansion close to the coefficient of linear expansion of the package.
Preferably, the piezoelectric element further has electrode patterns, and a position of a bump which connects the electrode patterns with the package is disposed point-symmetrically to a center of the piezoelectric element.
Preferably, the electrode patterns are formed so that a distance from a center of the piezoelectric element is xc2xd or less of a short side of the piezoelectric element.
Preferably, the surface acoustic wave element has the electrode patterns configuring a ladder-type filter. All positions of the bump which connects the electrode patterns with the package are preferably disposed at a side closer to a center of the piezoelectric element than a resonator disposed at a side of the short side of the ladder-type filter.
In order to solve the above deficiency, according to a second aspect of the present invention there is provided a surface acoustic wave device, comprising a package having a coefficient of linear expansion; and two piezoelectric elements forming a surface acoustic wave element, and mounted on the package by a flip chip bonding. Each of the two piezoelectric elements has different coefficients of linear expansion in a direction of propagation of surface acoustic waves generated by an interdigital electrode of the surface acoustic wave element and in a vertical direction thereto, and having a long side existing to a direction having a coefficient of linear expansion close to the coefficient of linear expansion of the package, and further having respective different central frequencies.
Preferably, ground electrodes of the surface acoustic wave element formed respectively on the two piezoelectric elements are common in the package.
Preferably, the ground electrodes of the surface acoustic wave elements formed respectively on the two piezoelectric elements are independent in the package.
Preferably, the surface acoustic wave element is a double mode type filter, in which an input side ground electrode and output side ground electrode of the filter are separated in the package.
Preferably, the surface acoustic wave element formed in any one of the two piezoelectric elements is a cascade-connected double mode type filter, in which an input side ground electrode and output side ground electrode of the filter are separated in the package.
The piezoelectric element may be cut out from a single crystal having X, Y, and Z crystal axes, and the X crystal axis agrees with a direction of propagation of the surface acoustic waves.
The piezoelectric element may be cut out from a LiTaO3 single crystal rotated around the X axis at a rotated angle from the Y axis to the Z axis, the rotated angle being in a range between 40xc2x0 and 44xc2x0.
The above and other objects, aspects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.